Initiation of detonation by steady planar incident shock waves

The initiation of detonation by planar shocks is studied in a vertical shock tube in which a removable diaphragm allows the generated shock to be transmitted into the gas mixture, without any reflection at the interface. Streak schlieren photography confirms that a quasi-steady shock reaction complex is formed prior to the shock acceleration phase. The steady phase enabled the induction delay time to be measured in a direct manner, and microwave interferometry, along with pressure transducers, gave an accurate value for the delay time. The shock acceleration was determined from the locus of the exothermic reaction zone, and it is shown that the time coherence of energy release between particles entering the shock front at different times leads to the formation of reactive centers which are characteristic of mild ignition. Ignition delay data obtained by the incident shock method for oxyacetylene, diluted with nitrogen, are compared with those obtained by the reflected shock technique and shown to have advantages in high heat capacity systems.